Rheometers are used to determine the flow characteristics or behavior of rubbers, plastics, elastomers, and other polymers and viscous materials. Rheological measurements have for decades proceeded without any visualization of the field to which materials are subjected, particularly polymeric materials. The flow of complex materials is an example of nonlinear phenomena in nature. Structured fluids such as foams, colloids, micelles, granular materials and polymers display intricate dynamic behavior that is still defying complete description. Simple fluids show Newtonian behavior such as constant viscosity so that the shear stress σ is linearly proportional to shear rate ({dot over (γ)}).